DYNAMIC ANALYSIS OF THE CONCEPT OF RISERLESS DRILLING

ABSTRACT

While an offshore riser is the industry standard for drilling operations, the process becomes increasingly expensive in deeper waters. Fifty years of technological development and applied research in vertical offshore sectors do not reduce the direct and associated costs that are
increasingly impacting the economic viability of deepwater well drilling. In addition to the cost
of offshore risers, the tools and labor involved add enormous costs to the construction of deep
wells. The large amounts of mud accumulating in the 's deeper waters increase the potential
environmental impact in the event of equipment failure. The choice and design of a drilling rig
may be dictated by increasing variable loading on the deck and a greater amount of drilling mud
on the seabed surface, which may exceed the capacity of the well. Mud processing speeds,
mixing and bulk transportation requirements increase costs during operations, as do larger
volumes of mud stored or disposed of when drilling operations are suspended or fractures reach
their maximum depth.
Recent concepts of reducing the size of the riser or eliminating the riser when returning mud and
debris from the mudline to the rig are promising for deepwater operations. However, the
development costs can be as high as the operating costs of the deepwater risers for which they
are intended. A new concept was developed to enable deep water drilling and circulation using a
mud return pipe instead of an offshore riser. Connected drilling technologies enable the provision of return lines for drilling mud and associated tools. The cable ensures that debris returns to the surface during drilling, without the need for an offshore riser or pumps to support the seabed.
The concept includes a housing for the subsea rotary control device (RCD) as a ring barrier and a
modification of the subsea BOPE. Removing the vessel risers, mud volume and equipment
associated with this riser-less drilling system will increase the payload and deck space
requirements of the MODU. The impact of this riser-less drilling method, along with possible
improvements, could significantly increase the operating depth of the current generation floating
drilling fleet.
The method and concept are described in this project. The main support tools consist of a subsea
“educt return” (EdR) unit with an associated flexible composite pipe that enables the drill string
and debris return, allowing bi-directional flow. BOP and closed loop control box; Underwater BOP with integrated driving choke and safety lines; and “smart” drill pipe, BHA and powered downhole drills. In addition to removing tubing from a deep well structure, the methods and tools described in this project enable dual gradient drilling and could potentially be used in deep wells.
Drilling without extensions with material return.